Hydrolysis is a common enzymatic mechanism. There are numerous enzymes whose catalytic mechanism involves breaking a covalent bond in a substrate by the addition of a molecule of water across the bond. The reaction involves a nucleophilic attack by the water molecule's oxygen atom on a target bond within the substrate and results in a splitting of the water molecule across the target bond, thereby breaking the bond and generating two product molecules. This general mechanism applies to a wide variety of enzymes including phosphatases, lysophospholipases, glyoxalases, and phosphodiesterases.
The protein phosphorylation/dephosphorylation cycle is one of the major regulatory mechanisms employed by eukaryotic cells to control cellular activities. During protein phosphorylation, phosphate groups are transferred from adenosine triphosphate molecules to a protein by protein kinases. During protein dephosphorylation, phosphate groups are removed from a protein by protein phosphatases, using a hydrolytic mechanism. In this manner, phosphatases are involved in the control of many cellular signaling events that regulate cell growth and differentiation, cell-to-cell contact, the cell cycle, and oncogenesis.
Lysophospholipases (LPLs) are widely distributed enzymes that regulate intracellular lipids, and occur in numerous isoforms. These isoforms vary in molecular mass, the substrate metabolized, and the optimum pH required for activity. Small isoforms, approximately 15-30 kD, function as hydrolases; large isoforms, those exceeding 60 kD, function both as hydrolases and transacylases. A particular substrate for LPLs, lysophosphatidylcholine, causes lysis of cell membranes when it is formed or imported into a cell. LPLs are regulated by lipid factors including acylcarnitine, arachidonic acid, and phosphatidic acid. Thus, the activity of LPLs is regulated by signaling molecules important in numerous pathways including the inflammatory response.
The glyoxylase system consists of glyoxylase I, which catalyzes the formation of S-D-lactoylglutathione from methyglyoxal, a side product of triose-phosphate energy metabolism, and glyoxylase II, which hydrolyzes S-D-lactoylglutathione to D-lactic acid and reduced glutathione. Methyglyoxal levels are elevated during hyperglycemia and are likely due to increased triose-phosphate energy metabolism. Elevated levels of glyoxylase II activity have been found in human and in a rat model of non-insulin-dependent diabetes mellitus. The glyoxylase system has been implicated in the detoxification of bacterial toxins and in the control of cell proliferation and microtubule assembly. Elevated levels of S-D-lactoylglutathione, the substrate of glyoxylase II, induced growth arrest and toxicity in HL60 cells. Thus, the glyoxylase system, and glyoxylase II in particular, may be associated with cell proliferation and autoimmune disorders such as diabetes.
Sphingomyelin is a membrane phospholipid that is hydrolyzed to ceramide and phosphatidylcholine by the action of the phosphodiesterase, acid sphingomyelinase. Phosphatidylcholine is involved in numerous intracellular signaling pathways, while ceramide is an essential precursor for the generation of gangliosides, membrane lipids found in high concentration in neural tissue. Defective acid sphingomyelinase phosphodiesterase leads to a build-up of sphingomyelin molecules in lysosomes, resulting in Niemann-Pick disease.
The discovery of new human hydrolase-like molecules and the polynucleotides encoding them satisfies a need in the art by providing new compositions which are useful in the diagnosis, treatment, and prevention of cell proliferation disorder, and autoimmune disorders.